1. Field of the Invention
Embodiments of the present invention relates to compositions for dissolving or removing sulfur deposits from reservoir formations, production tubing and flow lines due to the production of sour gas and/or oil, and methods for making and using same.
More particularly, embodiments of the present invention relates to compositions for dissolving or removing sulfur deposits from reservoir formations, production tubing and flow lines due to the production of sour gas and/or oil, where the compositions include an effective amount of a reaction product of a diamine and an aldehyde or an aldehyde donor prepared at a diamine to aldehyde molar ratio between about 1:1 to about 1:6 and methods for making and using same.
2. Description of the Related Art
Sulfur deposition is becoming more pronounced due to the number of wells that are now sour. Canada is one of the biggest producers of sour gas wells in the world and as a result has had to come up with methods to remove the sulfur from reservoir formations, production tubing and flow lines.
Currently, sulfur solvents are either used on a continuous or batch wise basis to remove sulfur deposition from formation surfaces and equipment surfaces. The sulfur solvents typically used are based either on amines, aromatic hydrocarbons, or dimethyl disulfide (DMDS). The first two products have limited sulfur uptake at room temperature (approximately 2%) and typically retain between 5% and 15% sulfur after reacting with sulfur at 80° C. DMDS on the other hand may have up to a 100% sulfur uptake at room temperature. However, there are handling and HSE issues with using DMDS based products, which limits their application especially if the problem exists outside of Canada. Current suppliers are of these sulfur dissolution products include Weatherford International Inc. or Clearwater International LLC for aromatic hydrocarbon based products and DMDS based products, Baker Huges for amine based product, and Multi-Chem Group for aromatic hydrocarbon products.
Hydrogen sulfide (H2S) is a naturally occurring component during the production of crude oil and natural gas. The presence of H2S in oil and gas is challenging because it is corrosiveness, scale forming, toxic, and posses environmental and safety concerns. In Alberta, Canada one-third of the natural gas wells contain H2S. The main flow assurance problem associated with H2S is elemental sulfur formation. Precipitation of elemental sulfur occurs when the thermodynamic conditions of the process changes. High temperature and pressure favors the formation of polysulfides, whereas a decrease in temperature and pressure favors the reverse reaction of polysulfide to elemental sulfur and H2S1, shown in the reversible reaction below:H2S+SxH2Sx 
Deposition of solid elemental sulfur may block pores in producing formations and/or may block production tubing, pipelines, and/or surface equipment. Sulfur has a tendency to bond extensively to itself forming chains such as S8 molecules with a variety of molecular configurations. Sulfur also has the potential to act as a fairly strong oxidizing agent and causes corrosion in stainless steel equipment, particularly pitting and other forms of localized corrosion.
Different solvents have been used in the field to remove sulfur deposition from formation faces and production tubing strings. Based on the literature2, elemental sulfur is dissolved in sour gas either by a physical or chemical mechanism with hydrogen polysulfide. Ockelmann and Blount (1973) reported that physical solvents of high aromatic content had higher sulfur carrying capacity than lean hydrocarbons' and this agrees with what is commercially available today especially with the SULPH-AMAX® (a registered trademark of Weatherford/Lamb, Inc.) product line. Chemical solvents work as a sulfur solvent by reacting with the S8 ring. Most widely used chemical solvents are based on amines, which react with elemental sulfur in the presence of H2S to produce ionic polysulfide according to the following reaction:H2S+amine→amineH+.SH−
Dimethyl disulfide (DMDS) is another sulfur solvent that dissolves sulfur more effectively through both physical and chemical interaction. However, the handling of a DMDS is difficult because of its strong unpleasant odor. Currently there is a significant difference in sulfur uptake between DMDS and the amine/hydrocarbon systems currently available.
While there are several options for removing elemental sulfur deposits from reservoir formations, production tubing and flow lines, there is still a need in the art for other compositions that are effective at removing elemental sulfur deposits from reservoir formations, production tubing and flow lines.